Purification of naphthol



a mixture of 77% United States Patent Ofitice 8 Claims. (31. 260-621)The present invention relates extraction of naphthol from it, as well asto the purification of the product obtained; it relates particularly tothe obtaining of alpha-naphthol of a desired degree of purity frommixtures in which this heavy phenol is accompanied by other naphthalenederivatives.

The process according to the invention is particularly useful in theextraction of naphthols, in particular alphanaphthol, from mixturesobtained by the dehydrogenation of oxygenated cycloaliphatic compoundssuch as tetralone and/ or tetralol. When alpha-naphthol is thus madefrom alpha-tetralone and/or tetralol, it is generally accompanied byother substances which, in greater or lesser proportions, can include5,6,7,8-tetrahydro-alpha-napl1- thol, alpha-tetralone or1-keto-1,2,3,4-tetrahydronaphthalene, alphatetralol orl-hydroxy-1,2,3,4-tetrahydronaphthalene, naphthalene, 1,2- and1,4-dihydronaphthalenes, Tetralin, i.e. tetrahydronaphthalene, heavyproducts and tars.

The isolation of pure alpha-naphthols from such mixtures is a difficultproblem, for the known methods of distillation and of alkalineextraction do not give satisfactory results. While the distillationeasily separates the light fractions, consisting of the precipitatedhydrocarbons and the heavy products, it is unable to separate thetetralone from the naphthol; this is due to the fact that these twolatter compounds form (in the entire range of pressures useful indistillation) an azeotrope at the maximum boiling point; thus at 40 mm.Hg this gives of alpha-naphthol boiling at 187 C.; at 760 mm. Hg theazeotrope contains 74% of naphthol and boils at 290 to obtain naphtholof more than 74 to 77% content by ordinary distillation. As forazeotropic or extractive distillation, in the presence of othercompounds which modify the relative volatility of the tetralone and thenaphthol, these do not produce a satisfactory solution. Extraction bymeans of an alkaline wash entrains, together with the alpha-naphthol,the tetrahydronaphthol and a considerable proportion of the tetraloneand the tar. It is thus evident that the similarity between heproperties of naphthol, tetralone and tetrahydronaphthol renders theseparation of the naphthol very difiicult, and does not permit it to bepurified by the classical method.

The process according to the invention permits, by contrast apractically entire separation of naphthol from the accompanyingcompounds. The invention provides means which is readily applicable onan industrial scale for obtaining naphthol of any desired degree ofpurity from mixtures which can contain any proportion of tetralone,tetrahydronaphthol and/or other naphthalenic derivatives.

The process according to the invention consists in separating thenaphthol from the accompanying compounds by crystallisation in analiphatic or alicyclic hydrocarbon having at least five carbon atoms permoiecule.

The investigations which have led to the present invention havedisclosed the previously unknown fact that the alpha-naphthol behavesvery differently from the tetralone in certain aliphatic solvents. Ithas thus been found possible to separate the naphthol by fractionalcrystallisation, provided that additional solvents are used to a newprocess for the certain media containing C. It is thus not practicallypossible 3,316,131 Patented Apr. 25, 196

comprising alicyclic hydrocarbons preferably having to 12 carbon atoms,which may bear alkyl groups 2 substituents, or comprising aliphatichydrocarbons c more than 5 carbon atoms and boiling below 150 C.

Amongst the hydrocarbon solvents suitable for th crystallisation of thealpha-naphthol from such mixture the following are particularlysuitable: cyclohexane methyl-cyclohexane, cycloheptane, cyclopentane,methyl cyclopentane, Decalin (decahydronaphthalene) and th commercialsolvents known under the names of spirit and spirit E.

It is known that the latter spirits are made up of 1 major part ofaliphatic hydrocarbons and very little aro matic material; they arecharacterised by the followin; properties:

' SpiritC SpiritE The proportion of the solvent and the respectivetemperatures of solution and crystallisation vary, according to thecomposition of the mixture from which the naphthol is to be extractedand the nature of the solvent used, between limits which can bedetermined or chosen without difliculty by those skilled in the art.More often than not the proportion of solvent is 1 to 10 parts by weightper part of the mixture.

By way of non-limitative example, in the case of mixtures containing toof alpha-naphthol and 20 to 35% of tetralone, the proportions of solventare about 1 to 5 parts by weight per part of mixture to be treated. Thedissolution of the mixture in the solvent takes place generally at atemperature between the ambient and that at which the solution obtainedboils; temperatures near or equal to the boiling point of the solventare particularly recommended, for example about 80 C. with cyclohexane,C. for methyl cyclohexane, 100 to C. for spirit E. The crystallisationis carried out at a temperature below that of the dissolution, forexample between the ambient temperature and 0 C.

The separation according to the invention may becarried out in a singleprocedure, i.e. by extraction of the substances accompanying thenaphthol by means of solvent at a selected temperature, for example theambient; the naphthol containing mixture must then be agitated with thesolvent sufliciently long to bring about the solution of the compoundsother than the naphthol.

The results of the separation according to the invention are better inproportion to the amount of naphthol in the mixture. It is especiallypreferable that this amount should be above 50% by Weight or better,60%. Therefore, according to a preferred method of carrying out theinvention applicable to mixtures containing less naphthol, the mixtureis first enriched with naphthol by distillation, after which theconcentrated fraction is treated with the aliphatic or alicyclic solventso as to separate the crystallised naphthol.

In this latter method of carrying out the invention it is desired tohave the least possible tetral-one in the fraction enriched withnaphthol. If the mixture initially contains much tetralone, for examplemore than 0.5 times the amount of alpha-naphthol, it is recommended torecover, during the distillation, a fraction as poor as possible intetralone and rich in naphthol, i.e. :a fraction of the composition nearor equal to that of the tetralone-naphthol azeotrope.

L is possible to obtain an overall yield of nearly 100% iaphtholextracted if, after the first separation of the hthol, the solvent isremoved from the mother liquor the residue is subjected to an enrichmentwith mph 1, by fractional distillation, and retreated with solvent is tobring about recrystallisation of the naphthol. f the initial mixture tobe treated has to be enriched fractional distillation, as indicatedabove, there may be ed to it the residual mixture mentioned in thepreviparagraph, the resultant mixture then being submitted enrichmentand the operations being carried out itinuously. Fhe purity of thealpha-naphthol crystallised according Lhe invention can be furtherimproved by a second crysisation in one of the solvents used accordingto the ention. It is thus of value to operate with the same vent as inthe primary crystallisation and to work in a thodical cycle; the puresolvent is used in the second stallisation of which the mother liquor isemployed in first. The number of successive crystallisations can coursebe increased, but this is not generally necessary; perience of carryingout the process shows that after successive crystallisations thealpha-naphthol does not ntain more detectable impurities. The method ofcarrying out the invention will be illusited by the followingnon-limitative examples.

Examples 1 l0 8 The operations of separation of alpha-naphthol, comisingtwo successive crystallisations, were carried out ith different solventson the same initial mixture which intained, by Weight:

1 each of these eight examples, the results of which are hown in Table Ibelow, the initial mixture was treated rith the mother liquor derivedfrom a purification by rerystallisation of previously preparedalpha-naphthol with resh solvent. In other words, the two columns ofyield nd melting points of naphthol obtained, shown in Table I, ndicatethe results which can be obtained in a continuous vrocess where thefirst crystallisation is carried out with he mother liquor of the secondone, this latter using fresh olvent recovered by distillation after thefirst crystallisaion.

The initial mixture was dissolved in the boiling mother iquor, afterwhich crystallisation was allowed to take )lace at about 22 C. Thecrystals obtained were dried and weighed and their melting pointdetermined. They were then taken up in the same quantity of freshboiling solvent; after a second crystallisation at 22 C., the weight andthe melting point of the naphthol crystals obtained were noted.

In Table 1 below the yield is the weight of naphthol crystallised,obtained for 100 kg. alpha-naphthol contained in the initial mixturetreated.

The column headed Proportion indicates the weight of solvent used in kg.per kg. of the initial mixture treated.

4 It is seen that the melting points of the products obtained,especially after the second crystallisation, are very near 96 C., i.e.,that of pure alpha-naphthol; the purity of the product obtained is thusvery good.

Example 9 The initial mixture had the following compositions by weight:

Percent Al pha-n aphthol Ttetrahydronaphthol 0.5 Alpha-tetralone 33.5Tars 1.0

1945 parts cyclohexane 219 parts tetralone containing 2% and 0.5% ofnaphthol 486 parts of a new mixture enriched in alpha-naphthol 9 partsof residue 486 parts of enriched mixture contained:

of tetrahydronaphtholi Percent Alpha-naphthol 74.1 Tetrahydronaphthol0.2 Alpha-tetralone 25.3 Tars 0.4

This mixture in its turn was treated with cyclohexane and there wasobtained very pure naphthol in a yield of 61.2%; the total yield of thetwo treatments with respect to the 650 parts by weight of initialnaphthol amounted to 77.8%.

The treatment was repeated a third time, on the fraction rich innaphthol, obtained by distillation of the mother liquor remaining afterthe second treatment, the entire yield was then raised ot 90.5%.

Example 10 A mixture containing:

Percent Alpha-naphthol 61.3 Dihydronaphthalene 21.6 Tetralone 8.2vTetralin 2.2. Tars 6.7

TABLE I Solvent 1st Crystallisation 2nd crystallisation Example No.Nature Iro- Yield M.P. Yield M.P.

portion (percent) C.) (percent) C.)

3 "do 3 61 94. 55 55. (i 95. 1 4 Metl1ylcyclohexane 2 64 94. 6 60.994.95

5. Spirit E 3 64. 2 92. 9 G4. 0 94. 6 6... d 5 57 94. 6 50. 3 94. 7Spirit C 5 55.2 94.7 8 Decalin..- 1.5 52.3 94.5

hydrogenated naphthalenes, which consists in: treating the mixture witha liquid saturated hydrocarbon, having 5 to 12 carbon atoms in itsmolecule, in an amount sufiicient for dissolving the components of themixture other than naphthol; allowing the naphthol to crystallize; andseparating the crystallized naphthol from its mother liquor.

2. Method for extracting alpha-naphthol from mixtures of the same withone or more materials selected from the group consisting of5,6,7,8-tetrahydro-alpha-naphthol, 1-keto*l,2,3,4-tetrahydronaphthalene,l-hydroxy-1,2,3,4- tetrahydronaphthalene, 1,2-dihydronaphthalene,1,4-dihydronaphthalene, tetrahydronaphthalene, naphthalene and tars,which consists in: treating the mixture with a liquid saturatedhydrocarbon having 5 to 12 carbon atoms in its molecule, selected fromthe group consisting of aliphatic and alicyclic hydrocarbons, in anamount sufiicient for dissolving the components of the mixture otherthan .alpha-naphthol; allowing the alpha-naphthol to crystallize; andseparating the crystals of alpha-naphthol from their mother liquor.

3. Method according to claim 2, wherein the amount of said liquidsaturated hydrocarbons is of 1 to 5 parts by weight per part of themixture treated, while the dissolution of the mixture is effected at atemperature comprised between ambient temperature and the boiling pointof the hydrocarbon, the crystallizing and separating of the crystals ofalpha-naphthol being carried out at a temperature between C. and theambient one.

4. Method for the extraction of alpha-naphthol from mixtures of the samewith alpha-tetralohe, which consists in: treating the mixture with aliquid saturated hydrocarbon having in its molecule at least carbonatoms, in

:an amount sufiicient to dissolve the tetralone; allowing thealpha-naphthol to crystallize in the solution thus obtained; andseparating the crystals of alpha-naphthol from the solution.

5. Method for the extraction of alpha-naphthol from mixtures of the samewith alpha-tetralone, which consists in: treating the mixture with aliquid saturated hydrocarbon having in its molecule 5 to 12 carbonatoms, in

an amount of 1 to times the weight of the mixture to.

ambient; allowing alpha-naphthol to crystallize;

dissolve the same; allowing the alpha-naphthol to crysta lize in thesolution thus otbained; and separating the ct stals of alpha-naphtholfrom the solution.

6. Method for the extraction of alpha-naphthol fror mixtures of the samewith alpha-tetralone, which consis' in: treating the mixture with aliquid saturated hydrc carbon having in its molecule 5 to 12 carbonatoms, i an amount of 1 to 10 times the weight of the mixture t dissolvethe same in the heat, at a temperature which doe not exceed the boilingpoint of said liquid hydrocarbor cooling the solution thus obtained tocrystallize alpha naphthol; and separating the crystals of alpha-naphthofrom the solution.

'7. Method for extracting alpha-naphthol from mix tures of the same withalpha-tetralone, which consists in dissolving 1 part by weight of themixture in 1 to 10 part: of an aliphatic liquid hydrocarbons fractionboiling belovi C., the dissolution being efiected at a temperature abovethe ambient temperature but not exceeding the boiling temperature ofsaid hydrocarbons fraction; cooling the solution thus obtained down to atemperature between 0 C. and ambient, to allow alpha-naphthol tocrystallize; and separating the crystals of alpha-naphthol from thesolution.

8. Method for extracting alpha-naphthol from mixtures for the same withalpha-tetralone, which consists in: dissolving 1 part by weight of themixture in l to 10 parts of an alicyclic hydrocarbon selected from thegroup consisting of cyclopentane, methyl-cyclopentane, cyclohexane,methyl-cyclohexane, cycloheptane and decahydronaphthalene, thedissolution being effected at a temperature above the ambienttemperature but not exceeding the boiling temperature of said alicyclichydrocarbon; cooling the solution thus obtained to a temperature between0 C. and

and separating the crystals of alpha-naphthol from the solution.

No references cited.

LEON ZITVER, Primary Examiner. D. H. HELPER, Assistant Examiner.

1. METHOD FOR EXTRACTING NAPHIHOL FROM MIXTURES OF THE SAME WITH ONE ORMORE MATERIALS SELECTED FROM THE GROUP CONSISTING OF NAPHIHALENE,PARTIALLY HYDROGENATED NAPHTHALENES, AND HYDROXY AND KETO SUBSTITUTEDPARTIALLY HYDROGENATED NAPHTHALENES, WHICH CONSISTS IN: TREATING THEMIXTURE WITH A LIQUID SATURATED HYDROCARBON, HAVING 5 TO 12 CARBON ATOMSIN ITS MOLECULE, IN AN AMOUNT SUFFICIENT FOR DISSOLVING THE COMPONENTSOF THE MIXTURE OTHER THAN NAPHTHOL; ALLOWING THE NAPHTHOL TOCRYSTALLIZE; AND SEPARATING THE CRYSTALLIZED NAPHTHOL FROM ITS MOTHERLIQUOR.